Method of treating molten material by use of a lance

ABSTRACT

The disclosure relates to a method of treating a molten bath of material such as iron by using a lance for supplying a treating material usually in a fluid state to the bath where the lance is cooled with a non-aqueous coolant which has a boiling point substantially higher than that of water or which undergoes dissociation at a temperature that is substantially higher than the boiling point of water for substantially the same pressure conditions.

United States Patent 1 Pelczarski et al.

11 3,744,780 [451 July 10, 1973 METHOD OF TREATING MOLTEN MATERIAL BY USE OF A LANCE Inventors: Eugene A. Pelczarski; Paul J. Larosa,

both of Allison Pk.; James A. Karnavas, Pittsburgh, all of Pa.

Applied Technology Corporation, Pittsburgh, Pa.

Filed: Jan. 7, 1972 Appl. No.: 216,191

Assignee:

U.S. Cl 266/34 L Int. Cl C2lb 3/02 Field of Search 266/34 L, 34 LM,

, 266/DIG. 41

References Cited UNITED STATES PATENTS l0/l962 Sands 266/34 R Primary Examiner-Andrew R. .luhasz Assistant Examiner-W. R. Briggs Attorney-John W. Malley, George M. Sirilla et al.

22 Claims, 2 Drawing Figures FZOW CONTROL Vfll V 1 6001/06 mw'in, //v I 44 METHOD OF TREATING MOLTEN MATERIAL BY USE OF A LANCE BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION The present invention relates to a method of treating a bath of high temperature material such as molten iron wherein a lance is employed to supply a material to the bath. More specifically, the invention provides a novel process for cooling the lance so as to permit the submerging of the lance beneath the surface of the bath to thus effect more efficient contact and intermixing of the treating material with the bath material. One of the features of the method of the present invention will be seen to be its capability of reducing the hazards that have commonly been experienced in using the previously known lance systems.

In the preparation of a wide variety of products it has been found desirable and often necessary to add ingredients to or chemically treat a material while the material is in a molten state. For example, in the production of certain grades of metal such as steel, it has been the practice to react the molten metal with an oxidizing material to accomplish the removal of impurities from the molten iron bath. In particular, in the process of steel making, a lance device is employed to direct a relatively high pressure flow of oxygen onto the surface of a molten bath of iron to reduce the carbon content of the iron.

The lances employed in a metal refining process are, of course, exposed to extremely high temperatures which has, in the past, rendered it unsafe to employ the lances over extended periods since the high temperatures adversely effect the lance material. Primarily, the lances are employed to direct a gas stream which may contain solids against the surface of the bath so that, as will be evident, the contact efficiency is relatively limited as an appreciable amount of the gas will be lost from the system without reacting with the bath material thus requiring additional time to complete the gas treating step.

Presently, it is the practice to use water as the cooling medium for the lances which are provided with jackets or passages so disposed as to cool the lance components, particularly the outside wall which is subjected to the greatest heat influx. Such systems, however, require constant monitoring since, if the lance fails, as can occur should the lance inadvertently come into contact with the molten metal, water would be introduced into the bath which can result in potentially explosive reactions as a result of the generation of large volumes of water vapor and other gases such as hydrogen and carbon monoxide. It can be readily appreciated that since the molten iron is being maintained at a temperature in excess of 2200F, the evolution of gas beneath the surface of the molten iron can result in the splattering of the molten iron from the vessel into the surrounding environment.

The lance treating system of the present invention minimizes and even eliminates a number of the problems occurring in this field as well as provides several significant advantages which will reduce operating costs and enable the bath treating process to be carried out much more safely than has heretofore been possible.

Broadly stated, the method consists in employing a non-aqueous medium as a coolant for the lance with the coolant being pumped through a closed-looped system. It has been found that by substituting a coolant having a low melting point and a high boiling point relative to the boiling point of water in conjunction with the closed-looped transfer system, a lance may be submerged directly into the molten material of a bath thus greatly improving the contact efficiency of the system while minimizing the possibility of a hazardous condition occurring should the lance fail and the coolant material come into contact with the molten bath material. More specifically, it has been found that by employing an alkali metal or a number of alloys of the alkali metals as well as other metals having low melting points and relatively high boiling points, the lance can be safely used in the open hearth steel refining process by submerging the lance directly into the molten iron.

Previously it has been the practice to construct the lances from material having relatively high thermal conductivity such as, for example, from copper. By employing the method of the present invention, however, material such as steel can be employed in the lance construction even though these materials have a lower thermal conductivity since surface boiling of the coolant material will be avoided where the coolant has a relatively high boiling point relative to that of water under similar pressure conditions. It will be evident that, because of the higher strength of steel, higher op erating temperatures can be achieved thus affording savings in the time necessary to effect the treatment of the molten bath as well as corresponding savings in energy consumption. In particular, when water has been used as the cooling fluid in a lance, the water bulk temperature had to be kept below its boiling point to avoid decreasing the heat transfer rate resulting from the occurrence of a film type insulation which results from the boiling of the water adjacent to the interior walls of the cooling passages of the lance. Thus, it has been necessary to operate the lance with a high temperature difference being maintained between the molten material and the cooling water which results in a large amount of heat transfer from the molten material to the water coolant. Such heat losses are avoided with the method of the present invention by the use of a high boiling point non-aqueous coolant which will permit the lance to operate at a higher temperature.

The foregoing and other objects and advantages will become apparent as further consideration is given to the following detailed description and, in that description reference will be had to the accompanying drawmgs.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of the system of the present invention; and

FIG. 2 is a schematic illustration of the lance in operation.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, there is illustrated in FIG. I a closed-loop cooling system for a lance which is schematically illustrated at 10. The lance 10 may be of any conventional construction such as that disclosed in U.S. Pat. No. 3,059,913 granted Oct. 23, 1962. Such lances generally consist of a centrally located tubular passage 12 which is connected at one end to a suitable conduit 14 which in turn is connected to a supply source of treating oxygen where the lance is to be used for the treatment of iron.

Adjacent to the passage 12 is a passage 16 which preferably is of annular cross-section and disposed concentrically about passage 12. Another passage 18 with a shape similar to passage 16 but of larger diameter is also concentrically disposed with respect to the passage 12.

A coolant material is introduced into passage 18 from conduit 20 and passes in heat transferring relationship with the outer wall 22 of the lance l0. Communication between passage 20 and passage 16 is established adjacent the lower end 24 of the lance so that the passage of the coolant will be generally from the upper or rear end 26 of the lance toward the lower end 24 along passage 18 and then back toward end 26 where the coolant is passed out of the lance through a suitable conduit schematically indicated at 28. The volume capacities of the respective passages and conduits of the lance and coolant supply system will of course be determined by the temperature conditions that are encountered in the treatment of various molten materials as will be apparent to those skilled in this art.

The operation of the system of FIG. 1 is as follows:

Relatively cold coolant is pumped into the lance 10 by pump 30 through suitably insulated valved conduits. The hot coolant is drawn from the lancethrough conduit 28 and delivered to a water-cooled heat exchanger 32. During steady operation of the system, valve 34 in bypass conduit 36 is closed and valve 38 in conduit 20 is open.

From the heat exchanger 32 relatively cold" coolant is delivered to a reservoir 40 ready for recycling through the pump 30.

The temperature of the cold coolant exiting from the heat exchanger can be controlled by adjusting the cooling water rate of feed into the heat exchanger 32. A conventional temperature sensing device 42 is suitably positioned to sense the temperature of the coolant exiting from the heat exchanger and is used to operate a flow control valve 44 which regulates the flow of cooling water into the heat exchanger 32. While regulation of the heat exchanger operation is usually adequate to provide safe control of the temperature of the lance 10, it is highly desirable that control of the rate of flow of the coolant through the passages 18 and 16 of the lance 10 itself be regulatable. Thus, a temperature sensing device 46 is employed to sense the temperature of the lance adjacent its lower end 24 so that when the temperature of the lance increases, the temperature sensing device 46 will provide a signal to control the speed of the motor of the pump to correspondingly increase the flow of coolant through the lance. The temperature sensing device 46 can also be utilized to provide a signal to an audiovisual alarm 48 which will alert the operator of the system when the lance temperature reaches a predetermined maximum at which point the lance would be removed from the molten bath.

As previously noted, the present invention provides for the use of a non-aqueous coolant material having a relatively high boiling point as compared to the boiling point of water under comparable pressure conditions. A primary factor in selecting a coolant material is the inability of the coolant material to generate large volumes of gases in the event that the lance structure should rupture and the coolant material come into contact with the molten material in the bath. Thus, it has been found that where the molten bath material is metallic, a number of low melting point metals or metal alloys can be used as a coolant medium. Specifically, the present invention provides for the use of an alloy of 22 percent sodium and 78 percent potassium; 44.5 percent lead and 55.5 percent bismuth; or an alloy consisting of 97.5 percent lead with 2.5 percent magnesium. In addition, an alloy which is a mixture of 18.4 percent tin, 32.2 percent lead and 49.2 percent bismuth is useful. Also the alloy commonly known as Woods metal which is a mixture of lead, cadmium, bismuth, and tin is particularly useful since this alloy can safety be combined with a metallic molten material in the event that the lance structure fails and leaks its coolant into the molten bath. Other coolant materials that may be employed are those known as Newtons alloy, Rose s metal, and bismuth solder. The composition of these low melting alloys is presented in the following table.

Alloy %Bismuth %Tin %Lead %Cadmium D'Arcets Alloy 50 25 25 Newtons Alloy 50 18.75 31.25

Rose's Metal 50 22 28 Woods Metal 50 12.5 25 12.5

It will be obvious to those skilled in this art that by increasing the percent mixture of lead and bismuth in the foregoing alloys, the boiling point of the resulting alloy can be substantially increased.

Both lead and bismuth remain in a liquid state over wide temperature ranges (for lead: melting point 328- C., boiling point 1740C., approximately and for bismuth: melting point 271C, boiling point 1560C., approximately) which characteristic renders these metals very useful in a coolant alloy.

In addition to the foregoing, it has been found that some of the alkali metals such as lithium and sodium can be profitably used as coolant mediums since they remain in a liquid state over a broad range of temperatures (for lithium, melting point 180.5C., boiling point 1330C., approximately; for sodium: melting point 97.8C., boiling point 892C, approximately).

A number of the well known alkali salts such as sodium nitrite, sodium nitrate and potassium nitrate can be employed as the coolant medium since they are liquid from about 280F. to approximately 1 F. at which latter temperature the salts usually undergo slow thermal decomposition resulting in the evolution of a relatively small amount of nitrogen gas.

As will be evident, when the foregoing materials are used as the coolant medium, the reservoir 40 must be provided with heating coils since these materials are not in a liquid state at ambient temperatures. In addition, where the metals and metal alloys are being used as the coolant medium, the pump 30 must be of the electromagnetic type or other suitable means must be employed to move the coolant medium through the loop at a rate sufficient to effect the cooling of the lance surface that comes into contact with the molten bath.

In addition to the foregoing materials, thermal liquids such as diphenyldiphenyloxide which is sold under the trademark Dowtherm A and O-dichlorobenzene which is sold under the trademark Dowtherm E by the Dow Chemical Company are suitable for a number of applications particularly where non-metallic materials are being treated in a molten state by a lance. Also mineral oils such as those sold under the trademarks Mobiltherm 600 and Mobiltherm light marketed by the Socony Mobil Oil Company are intrinsically safe coolant mediums since in the high temperature ranges involved in molten bath treating process only small amounts of gases will be evolved should these mediums come into contact with the high temperature baths.

In FIG. 2, the lance is illustrated .in its operating position with its lower end inserted beneath the surface 50 of a molten bath of material 52 in a vessel 54. A coolant medium is being supplied to the lance 10 while the lance tip is submerged into the molten bath 52 through conduit and taken off through conduit 28. A treating fluid is being supplied to the bath 52 by way of conduit 14 and lance l0. Depending on the type of material and the temperature of the molten bath 52, one of the coolant mediums as described above when pumped at a sufficient rate through the cooling passages of the lance 10 will permit the insertion of the lance beneath the surface 50 of the bath which will result in greatly increased contact efficiency between the treating gas and molten material retained in the vessel with the corresponding advantages of a minimum of loss of treating fluid to the surrounding environment and reduced operating time requirements stemming from the increased contact efficiency. In addition should lance failure occur, a hazardous situation will be avoided where the coolant mediums described above are employed. It will also be evident that energy is conserved since heat loss from the molten material to the coolant is reduced where a high boiling point coolant as discussed above is employed.

As will be evident from the foregoing discussion, when a non-aqueous coolant is used which permits submerging operation of the lance at a higher temperature, the lance will not be subjected to an extreme thermal shock as is the case where water is used and the lance is inserted either accidentally or for a brief period into the molten bath.

While the method of the present invention has been described above in terms of particular embodiments, it will be understood by those skilled in the art that modifications thereof are possible and such are intended to be included within the scope and spirit of this invention as defined in the appended claims.

What is claimed is:

1. in a method of treating a molten bath with a lance of the type having a fluid delivery portion for supplying a treating fluid to the bath and separate passage means for a coolant material located to be in heat transferring relation with said fluid delivery portion, the improvement comprising the step of pumping, in liquid form, through the said separate passage means of the lance a non-aqueous coolant material having a boiling point substantially higher than the boiling point of water when under substantially the same pressure.

2. The method as claimed in claim 1 including the step of submerging the fluid delivery portion of the lance in the molten bath.

3. The method as claimed in claim 1 wherein said coolant material is an alkali metal.

4. The method as claimed in claim 3 wherein said coolant material is sodium.

5. The method as claimed in claim 3 wherein said coolant material is lithium.

6. The method as claimed in claim 1 wherein said coolant material is a metallic alloy, a major constituent of which is bismuth.

7. The method as claimed in claim 6 wherein the minor constituent of said metallic alloy is lead.

8. The method as claimed in claim 1 wherein said coolant material is a metallic alloy, a major constituent of which is potassium.

9. The method as claimed in claim 8 wherein the minor constituent of said metallic alloy is sodium.

10. The method as claimed in claim 8 wherein said metallic alloy is composed approximately of 78 percent potassium and 22 percent sodium.

11. The method as claimed in claim 1 wherein said coolant material is a metallic alloy, a major constituent of which is lead.

12. The method as claimed in claim 11 wherein the minor constituent of said metallic alloy is magnesium.

13. The method as claimed in claim 12 wherein said metallic alloy is composed approximately of 97 percent lead and 2.5 percent magnesium.

14. The method as claimed in claim 1 wherein said coolant material is a metallic alloy of lead, cadmium, bismuth, tin and indium.

15. The method as claimed in claim 1 wherein said coolant material is a mineral oil.

16. The method as claimed in claim 1 wherein said coolant material is diphenyldiphenyloxide.

17. The method as claimed in claim 1 wherein said coolant material is o-dichlorobenzene.

18. In a method of treating a molten bath with a lance of the type having a fluid delivery portion for supplying a treating fluid to the bath and separate passage means for a coolant material located to be in heat transferring relation with said fluid delivery portion, the improvement comprising the step of pumping through the said passage means of the lance a molten inorganic salt.

19. The method as claimed in claim 18 including the step of submerging the fluid delivery portion of the lance in the molten bath.

20. The method as claimed in claim 18 wherein said molten salt is sodium nitrite.

21. The method as claimed in claim 18 wherein said molten salt is sodium nitrate.

22. The method as claimed in claim 18 wherein said molten salt is potassium nitrate.

* t 1' I Q 

2. The method as claimed in claim 1 including the step of submerging the fluid delivery portion of the lance in the molten bath.
 3. The method as claimed in claim 1 wherein said coolant material is an alkali metal.
 4. The method as claimed in claim 3 wherein said coolant material is sodium.
 5. The method as claimed in claim 3 wherein said coolant material is lithium.
 6. The method as claimed in claim 1 wherein said coolant material is a metallic alloy, a major constituent of which is bismuth.
 7. The method as claimed in claim 6 wherein the minor constituent of said metallic alloy is lead.
 8. The method as claimed in claim 1 wherein said coolant material is a metallic alloy, a major constituent of which is potassium.
 9. The method as claimed in claim 8 wherein the minor constituent of said metallic alloy is sodium.
 10. The method as claimed in claim 8 wherein said metallic alloy is composed approximately of 78 percent potassium and 22 percent sodium.
 11. The method as claimed in claim 1 wherein said coolant material is a metallic alloy, a major constituent of which is lead.
 12. The method as claimed in claim 11 wherein the minor constituent of said metallic alloy is magnesium.
 13. The method as claimed in claim 12 wherein said metallic alloy is composed approximately of 97 percent lead and 2.5 percent magnesium.
 14. The method as claimed in claim 1 wherein said coolant material is a metallic alloy of lead, cadmium, bismuth, tin and indium.
 15. The method as claimed in claim 1 wherein said coolant material is a mineral oil.
 16. The method as claimed in claim 1 wherein said coolant material is diphenyldiphenyloxide.
 17. The method as claimed in claim 1 wherein said coolant material is o-dichlorobenzene.
 18. In a method of treating a molten bath with a lance of the type having a fluid delivery portion for supplying a treating fluid to the bath and separate passage means for a coolant material located to be in heat transferring relation with said fluid delivery portion, the improvement comprising the step of pumping through the said passage means of the lance a molten inorganic salt.
 19. The method as claimed in claim 18 including the step of submerging the fluid delivery portion of the lance in the molten bath.
 20. The method as claimed in claim 18 wherein said molten salt is sodium nitrite.
 21. The method as claimed in claim 18 wherein said molten salt is sodium nitrate.
 22. The method as claimed in claim 18 wherein said molten salt is potassium nitrate. 